The present invention relates to high speed generators and, more particularly, to systems and methods for fastening wire coils to the rotors of such generators.
Generator systems that are installed in aircraft may include three separate brushless generators, namely, a permanent magnet generator (PMG), an exciter, and a main generator. The PMG includes permanent magnets on its rotor. When the PMG rotates, AC currents are induced in stator windings of the PMG. These AC currents are typically fed to a regulator or a control device, which in turn outputs a DC current. This DC current next is provided to stator windings of the exciter. As the rotor of the exciter rotates, three phases of AC current are typically induced in the rotor windings. Rectifier circuits that rotate with the rotor of the exciter rectify this three-phase AC current, and the resulting DC currents are provided to the rotor windings of the main generator. Finally, as the rotor of the main generator rotates, three phases of AC current are typically induced in its stator windings, and this three-phase AC output can then be provided to a load such as, for example, electrical aircraft systems.
Because the generators installed in aircraft will often be variable frequency generators that rotate in the speed range of 12,000 rpm to 24,000 rpm, large centrifugal forces are imposed upon the rotors of the generators. Given these stressful operating conditions, the rotors of the generators should be carefully designed and manufactured, both so that the rotors are reliable and also so that the rotors are precisely balanced. Improper balancing in particular can result not only in inefficiencies in the operation of the generators, but also in a risk of failure of the generators.
Among the important components in rotors that should be carefully designed and manufactured in order to guarantee robustness and proper balancing of the rotors are the wire coils of the rotors. The centrifugal forces experienced by the rotors are sufficiently strong as to cause bending of the wires of these coils, which over time can result in mechanical breakdown of the wires. Additionally, because the coils are assemblies of individual wires that can move to some extent with respect to one another and with respect to the remaining portions of the rotors, the coils constitute one of the significant potential sources of imbalance within the rotors. The stresses and movement experienced by the wire coils are particularly problematic at the end turns of the coils, at which wires loop from first directions to second directions on the poles supporting the wires.
In order to guarantee robust wire coils and to minimize the amount of imbalance in the rotors that occurs due to the wire coils, the process of initially wrapping the wires of the coils onto the rotors is typically a time-intensive, expensive task. To keep the wrapped coils to within specified tolerances, complicated tooling equipment and an involved process of utilizing shims to guarantee sufficient internal pressure among the wires of the coil are required. Often, the wrapping process involves a significant amount of trial and error before all of the multiple coils on a multi-pole generator are properly configured to have the desired balancing and other characteristics. The difficulty of the wrapping process is greatest at the end turns of the coil wires.
Hence, there is a need for a new system and method for supporting and retaining the wire coils in rotors, particularly at the end turns of the coils. There further is a need for a system and method for end turn retention in which the coil wires at the end turns are positioned accurately and held reliably in position. There additionally is a need for such a system and method whereby the wrapping process is made simpler, more accurate and repetitive, and more cost-effective.
The present inventors have recognized that end turn supports employed on rotors can be designed to include flanges that provide support to the end turns to limit movement of the wires radially inward. By coupling these supports to end cap hats that limit movement of the wires radially outward, pressure is generated upon the wires in between the flanges and the end cap hats causing the wires to become packed and thereby more robust. At the same time, the coupling of the supports to the end cap hats forces the wires into precise desired locations, thereby improving rotor balance and robustness and simplifying the wrapping process.
In particular, the present invention relates to a rotor for use in a high speed generator, where the rotor includes a shaft extending axially through the rotor, a plurality of spokes extending radially from a location along the shaft and a plurality of supports, where each one of the supports is positioned proximate a respective one of the spokes. The rotor further includes a plurality of coils of wire windings, each wrapped around a respective one of the supports and a respective one of the spokes, and at least one cap device coupled to ends of the spokes away from the shaft. The at least one cap device prevents the wire windings of the coils from moving outward away from the shaft beyond outer radial limits. Each support is coupled to the at least one cap device, and each support extends radially inward along its respective spoke from the at least one cap device to at least a respective inner limit. Each support includes at its respective inner limit a respective flange protruding away from the respective spoke, and each flange prevents the wire windings of the respective coil from moving beyond the respective inner limit towards the shaft.
The present invention further relates to a support for implementation on a spoke extending outward radially from a shaft of a rotor. The support includes a U-shaped main portion having an outer face and an inner face, where the support is configured so that the inner face of the support is in physical contact with the spoke when the support is supported thereby, and where the support is further configured to support a wire coil that is wrapped around the support along the outer face. The support further includes first and second sides of the U-shaped main portion that are substantially transverse with respect to the outer and inner faces and also with respect to a channel along the inner face through the U-shaped main portion, the channel being configured to receive the spoke. The support additionally includes a flange proximate the first side of the U-shaped main portion and extending outward away from the channel beyond the outer face. The support is configured to be positioned on the spoke so that the first side is closer to the shaft than the second side, and is additionally configured to allow for coupling of the support to a cap hat.
The present invention additionally relates to a generator including a stator and a rotor that is rotatably coupled within the stator. The rotor includes a shaft extending axially through the rotor, a plurality of appendages extending radially outward from the shaft, and a plurality of wire coils that are supported away from the shaft by the plurality of appendages. The rotor further includes a first means for preventing outward radial movement of wires of the wire coils beyond respective outer limits, and a second means for preventing inward radial movement of wires of the wire coils beyond respective inner limits. At least one of the first means and second means is secured to the plurality of appendages and, when only one of the first means and second means is secured to the plurality of appendages, the remaining other means is further secured to that one of the first and second means that is secured to the appendages.
The present invention further relates to an end cap device for implementation in a rotor including an appendage extending outward radially from a shaft of the rotor and further including a support positioned on the appendage, wherein the support is capable of supporting end turns of a wire coil of the rotor and includes a flange at an inner radial position that limits movement of the end turns radially inward toward the shaft. The end cap device includes a physical barrier, a first fastening element by which the end cap device is coupled to the appendage, and a second fastening element by which the end cap device is coupled to the support.
The present invention additionally relates to a method of retaining wires of a coil within a desired radial region relative to a shaft of a rotor. The method includes positioning at least one of a support and an additional element on a first appendage extending radially from the shaft, where the at least one support and additional element includes a flange. The method additionally includes wrapping the wires of the coil onto the support, and providing a cap hat proximate an outer end of the first appendage away from the shaft. The method further includes attaching at least one of the cap hat and the support to the first appendage and, if only one of the cap hat and the support is attached to the first appendage, further attaching the cap hat and the support to one another. The flange extends away from the first appendage and prevents movement of the wires of the coil toward the shaft beyond an inner limit, and the cap hat prevents movement of the wires away from the shaft beyond an outer limit.